As is known, many liquid or pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by creasing and sealing laminated strip packaging material. The packaging material has a multilayer structure comprising a base layer, e.g. of paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene. In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of oxygen-barrier material, e.g. an aluminium foil, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
A package is known which comprises:                a rectangular bottom wall which is crossed by a bottom transversal seal;        a rectangular top wall, which is crossed by a top transversal seal;        a rear wall which extends between corresponding first edges of top wall and bottom wall;        a front wall which is opposite to the rear wall and extends between corresponding second edges, opposite to first edges, of top wall and bottom wall; and        a pair of lateral walls interposed between bottom wall and top wall, and between rear wall and front wall.        
Furthermore, the package comprises a top transversal sealing band and a bottom transversal sealing band, which extend across respective top wall and bottom wall.
The top sealing band extends beyond the top wall into respective flat, substantially triangular flaps which are folded coplanar with and onto upper portions of respective lateral walls as of the top wall.
The bottom sealing band comprises a main portion folded over the bottom wall and a pair of lateral portions, which are folded over the main portion. The main portion is folded onto the bottom wall while the lateral portions form two respective flat, substantially triangular lateral bottom flaps of packaging material folded over the main portion.
Furthermore, the substantially triangular flaps are folded coplanar with and onto respective lateral portions of the bottom sealing band as of the lower portions of respective lateral walls.
In the known packages, flaps are shaped as isosceles triangles with two angles of 45 degrees or of more than 45 degrees.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; the web so sterilized is then maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a tube, which is fed vertically. Alternatively, the packaging material may be sterilized according to other techniques, e.g. by using low voltage electron beams.
In order to complete the forming operations, the tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections.
More precisely, the tube is sealed longitudinally and transversally to its own axis, so as to from pillow packs which will be eventually folded to form finished packages with a longitudinal seal and a top transversal seal and a bottom transversal seal.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are then filled with the food product and sealed.
In both the cases, known packages are produced starting from a basic unit of packaging material, which is, in the first case, a portion of a web of packaging material, and, in the second case, a precut blank.
In the first case, the web of packaging material comprises a succession of basic units and is:                folded into a cylinder to form a vertical tube and longitudinally sealed;        filled continuously with the food product; and        sealed transversely and cut into the basic units, which are than folded to form successive packages.        
In the second case, the basic unit is folded on the forming spindle, is filled with the food product and is sealed at the top and the bottom to form the package.
In both cases, the basic unit has a crease pattern, i.e. a number of crease lines which define respective folding lines, along which the packaging material is folded to form the finished packages.
The crease lines bound a plurality of panels, which define the walls and the flaps of the finished package, once that the basic unit has been folded.
In detail, the crease lines bound:                a pair of triangular first panels, which are interposed between, respective second triangular panels; and        a pair of triangular third panels, which are interposed between respective fourth triangular panels.        
First (fourth) panels define respectively the inner wall of top (bottom) flaps of finished packages whereas second (third) panels define respectively the outer walls of top (bottoms) flaps of finished packages.
Each first (third) panel is bounded by:                a segment of a first crease line, which defines the sides of the top (bottom) wall of the finished package; and        a pair of second crease lines, which extends between respective opposite ends of the segment and a common end on a third crease line.        
The third crease line is parallel to the first crease line.
The second crease lines are sloped relative to the first crease line and third crease line.
The base of first (third) panel is defined by the segment of the first crease line while the height of first (third) panel is defined by the distance between the first crease line and the third crease line.
Still more precisely, the first crease line defines with the second crease lines a pair of angles, which are greater than or equal to 45 degrees. In other words, the height of first (third) panels is greater than or equal to a half of the base of the same first (third) panels.
On one hand, a need is felt within the industry to reduce the amount of packaging material required for manufacturing a sealed package of a given volume, for evident economic reasons.
On the other hand, a need is felt within the industry to increase the volume of the package which can be formed from a given amount of packaging material, i.e. from a basic unit having a defined size.